Electric furnace



Patented Apr. 2, 1940 ELEUIBIC Daniel Gardner, Bueil- FUBNACE France,as-

Malmaison, signor to Maatschappij voor Thermo-Chemie N. V., Netherlands,a company of the Netherland! Application October 1l, In Great BritainSchirm.

This invention relates to electric furnaces intended for carrying outchemical, metallurgical or heat-treatment operations at hightemperatures.

In a furnace according to the present invention. generation of heat iseil'ected partly by the resistan encountered by the electric current inits ww: through the furnace, partly by small electric arcs generatedbetween the particles of l coarse granular material, into which theelectrodes project. Saidy material surrounds the furnace chamber inwhich the treatment is to be carricd out, in such amanner that the siseof the granules or particles decreases, from the inside towards theoutside, to an exceedingly small value. 'lhat is to say, the outer layerof the granular material is formed by line powder, which, in virtue ofthe very high intermediate ce between its particles, actually functionsas an ,o insulator, both electrically and thermally. The

granules of the inner layer of said material, however. have a relativelylarge size, say of 38 mm., so that electric arcs can be formed betweenthe same.

g5 In order that the above statements may be more readily understood,reference is had to the annexed drawing, which illustrates, in avertical sectional elevation, an electric furnace constructedin'accordance with the invention.

The furnace chamber proper is constituted by a vertical inner cylinder Iof graphite, petroleum coke, Carborundum, zirconium carbide or othermaterial suitable for the purpose. Said inner cylinder is surrounded,with'a narrow interspace, by

anoutercylinder 2ofsimilarmaterlal.

The furnace chamber i, the wall of which is provided with upwardlyinclined narrow passagesl,isiittedwithanimpellerscrew4 ofrefractcrymaterialsuch as graphite or petroleum coke, the pitch of said screwincreasing from the upper to the lower end. vThe screw impellerprojectsupwardlyintoahopperiforreceivingthematerialtobetreatemforinstancesuitably ground ore with the requiredfluxes.

Attheupperendtheinterspacebetweithe cylinders l and 2 communicates,through a conduit C, with a condensing chamber 1.

Thelowerendofthefurnacechamber opens some distance vertically above aconical screen l,

which serves for distributing the materialdischargedfromsaidchamberoveratablelsemred tothespindlelloftheimpellerl.,

The spindle I0 is driven at both ends. through themedium ofelasticcouplings il, I2,byworms 66 onshafts |3.i4 adaptodtoberotated,through1938, Serial No. 234.099 October 14, 1931 mitre wheels, by a commonshaft l5 in such a manner that the speed of the impeller I is say aboutone revolution per minute.

'Ihe outer cylinder 2 is surrounded, with a relatively wide interspace,by a refractory jacket It 5 of asbestos, magnesia, aluminium oxide orthe like, said jacket resting on a refractory slab i1, which itself issupported by a steel framework, to which also the bearings of thedriving gear are secured.

Electric current is introduced by electrodes I8 10 passed throughaperturesprovided, at different levels, in the Jacket I6. Saidelectrodes are ra dially slidable in suitably cooled bushes I9, and theinner end of each electrode is provided with a readily renewable wearingpiece of reduced cross- 15 section, said piece being preferably screwedinto the inner end of the main electrode.

The interspace between cylinder 2 and jacket Il is filled withgranularmatcrial.4 'I'he inner layer, i; e. the layer engaging the outerwall of 20 cylinder 2, consists of relatively coarse granules 2l ofcoke, graphite or the like. The outer layer,

i. e. the layer contacting with the 'inner wall of Jacket I6, consistsof soot (lamp black, carbon black) 2l, either or not mixed withmagnesia, 25 aluminium oxide or the like, and may be suitablycompressed, for instance, briquetted. The space intermediate said layers2B and 2| is filled with granular carbon, the size of these granules'decreasing, in outward direction, from a size corre- 30 sponding to thatof the granules of the layer 2l, to a size corresponding to that of theparticles of layer 2|.

The modus operandi of the described furnaceis asfollcws:` A

First, the electrodes It are moved inward, until their wearing piecesdirectly contact with the outer cylinder 2, whereupon the current isswitched on. The current will now flow principally through the cylinder2, which is thus quickly 4o heated to the required temperature.Thereafter, the screw impeller I is rotated, whereby the material to betreated Ais caused to slowly descend from the hopper l and through thereaction chamber to the bottom opening thereof'.l ,'When the furnace 45proper and the material therein have reached the4 desired temperatures,so that from that. moment onward the electrical energy supplied theelectrodes4 I8 only serve for maintaining said temperatures, theelectrodes are retracted a 50 little, whereby the current will pass forthe greater part through the coarse carbon granules, which by that timehave-already assumed a high temperature. As a en smalleleciz'icarcswillbeformedbetwcensaidgranules, 55

and the total strength of the current will be considerably reduced.

As stated, the very ne carbon powder (soot) on the outer side of thespace between cylinder 2 and jacket i6 acts as a heat insulator, so thatthe jacket i6 remains relatively cool. Besides, said powder also acts asan electric insulator, especially when magnesia or the like has beenadmixed thereto.

If desired, the electrodes can be adjusted by automatic means under thecontrol of a suitable thermostat.

The chamber 'l serves for collecting and condensing gaseous productsthat may be formed in the reaction chamber, for instance zinc vapours.

The increase of the pitch of screw 4 in downward direction prevents thematerials under treatment from clogging the reaction chamber.

What I claim is:-

1. An electric furnace comprising a base, a reaction chamber, an innerwall structure surrounding said chamber, said structure consisting of adouble-wall jacket, inclined channels in the inner wall of said jacketand connecting the reaction chamber with the inner space of the same, acondenser connected to said jacket, an outer wall encircling said innerwall structure, a space between said two walls, means for introducingthe charge into said chamber, means for dis charging the treated chargefrom the same, an insulating layer located adjacent to the inner surfaceof said outer wall and lling a section of said space, a plurality ofconcentric layers between said insulating layer and the outer surface ofsaid inner wall structure, said concentric layers forming the furnaceheating zone proper and Consisting of current conducting particles ofwhich the size gradually increases in the direction from said insulatinglayer towards said inner Wall structure and displaceable electrodessupported by said outer wall and protruding through said heatinginsulating layer into said heating zone proper.

2. An electric furnace comprising a base, a reaction chamber, an innerwall structure surrounding said chamber, said structure consisting of adouble-wall jacket, inclined channels in the inner wall of said jacketand connecting the reaction chamber with the inner space of the same, acondenser connected to said jacket, an outer wall encircling said innerwall structure, a space between said two walls, means for introducingthe charge into said chamber, a screw conveyor transporting the chargethrough the same, the pitch of said conveyor increasing from its upperto its lower end and means for discharging the treated charge from saidchamber, an insulating layer located adjacent to the inner surface ofsaid outer wall and filling a section of said space, a plurality ofconcentric layers between said insulating layer and the outer surface ofsaid inner wall structure, said concentric layers forming the furnaceheating zone proper and consisting of current conducting particles ofwhich the size gradually increases in the direction from said .in-

wall, a plurality of at least three concentric layers of currentconducting particles between said insulating layer and said innerwall-structure forming the heating zone of the furnace, the particlesize of said layers gradually increasing in the direction from saidinsulating layer towards said inner Wall structure and displaceableelectrodes supported by said outer wall.

DANIEL GARDNER.

